Sound recording system



Au 10, 1937. P, R, LENN 2,089,473

' SOUND RECORDING SYSTEM Filed July 22, 1935 HHHHHMHHHHHIW H goooaoooooofipooooaoom 42 'HHmmury INVENTOR.

Patented Aug. 10, 1937 ilhii'i'EE STATES PATENT @FMCE SOUND RECORDING SYSTEM Application July 22, 1935, Serial No. 32,567

2 Claims.

This invention relates to an improved system for recording acoustic waves upon a light sensitive film.

r The general object of the invention is to provide an improved means for controlling the action of a light valve.

A feature of the invention resides in the employment of constant currents of high frequency in the circuit controlling the mean recording position of a recording device.

Another feature of the invention resides in modulating the high frequency currents and controlling the output of the modulator by a direct current potential which is the product of the envelope of the signal currents.

An additional object of my invention is to provide a novel method of recording signal currents on a recording medium.

Other objects and the advantages of this invention will be apparent from the following description takn in connection with the accompanying drawing.

The accompanying drawing is a diagrammatic disclosure of my improved sound recording device.

Referring to the drawing by reference characters I have indicated my improved sound recording system generally at ID. A light source is shown at l2. From this source light is focused by a lens system It on apertures I 4 which are located in the pole pieces of a permanent magnet I5. The light is then focused by a lens system It through an aperture I? in a guide I8. A film I9 passing over sprockets 20 is subjected to light which passes through the aperture I'I. Flat conductors 2i and 22 arranged in the field of the magnet I constitute a light transmitting slot. The width of the slot formed between the con ductors 2i and 722 affects the exposure of the film l 9 to the light from the source I2.

The recording device thus briefly described is well known in the art and I do not wish to be limited to the use of this particular form of recording device.

Sound waves detected by the microphone 23 are suitably amplified in the usual amplifier unit 24 from which a portion of the signal currents pass through wires 25 and 26 to the input of a standard type amplifier unit which is diagrammatically shown and is enclosed by the dotted lines 21.

The output of the amplifier 24 is applied through wires 23 and 29 to the primary winding 34 of a transformer 35. The secondary winding 36 of the transformer is connected by wires 31 and 38 to the fiat light valve conductor members 2| and 22. The wire 38 has a potentiometer 39 Cir interposed therein. Thus it will be seen that a portion of the signal currents from the secondary winding 35 of the transformer 35 flows through the wire 37, through the conductors 2i and 22 and through the wire 38 back to the transformer 35.

The magnetic field due to the signal current flowing in the conductors 2i and 22 will react with the constant field due to the magnet i5 and cause the conductors 2I and 22 to vibrate and vary the width of the light transmitting slot in accordance with the instantaneous variations in the signal currents.

At 5 0 I have indicated diagrammatically a standard type electron coupled high frequency oscillator the output of which is impressed on the primary winding GI of a transformer 52 of a push-pull modulator I13. The output of the modulator i3 is impressed on the primary winding 44 of a transformer 35 of an amplifier unit 43 and the output of the amplifier unit 55 is impressed on the primary winding 41 of a transformer 48. The secondary winding 19 of the transformer 48 is connected by wires 50 and 5| to a full wave rectifier 52.

I may provide a bridge which includes terminals 54, 55, 56, 5?, 58, and 59. The terminal 58 of the bridge is connected by a wire 60 to one side of an A battery 5| or other source of constant voltage and the terminal 59 is connected by a wire 62 to the other side of the battery 6|.

The output of the rectifier 52 is connected by a wire 63 to the bridge terminal 54 and has interposed therein a choke coil 54 and a milliammeter 65. The choke 6t prevents the passage of any undesirable high frequency currents which might come from the oscillator Gil. The center tap of the secondary winding 49 of the transformer 48 is connected by a wire 56 to the terminal 55 of the bridge 53. The bridge terminal 5? is connected by a wire 6? to the center tap of the secondary winding 36 of the transformer 35 and the bridge terminal 551 is variably connected as at 88 to the potentiometer 39 by a wire 69. The potentiometer 39 is provided to balance the winding 38 and provide a center tap connection. In certain installations the bridge 53 may be omitted if desired. In this case the wire 63 would be directly connected to the wire 59 and the wire 66 would be directly connected to the wire 61 The secondary winding iii of the transformer 3| is connected by Wires II and 72 to a full wave rectifier I3, the output of which is connected by a wire it to one side of a condenser l5 and has interposed therein a choke coil 16. The center tap of the secondary coil H! of the transformer 3| is connected by a wire 11 to the other side of the condenser 15. The wire 11 is connected as at 18 to one end of a resistor 79. The opposite end of the resistor 19 is connected to the wire 14 as at 18 and is connected by a wire 80 to the grid resistors 8! of the push-pull modulator 43 and to the secondary winding 82 of the transformer 42. Furthermore the wire 1'! is variably connected as at 83 to the potentiometer 84 of the push-pull modulator 43. By adjusting the potentiometer 84 the amount of bias which is to be applied to the conductors 2i and 22 may be set at any desired maximum value. The condenser vl5, choke I6,

5 and resistance 19 form a filter system which together with the electron coupled oscillator 40 and the push-pull amplifier 43 results in a biasing current which is very free from instantaneous signal currents. As shown the oscillator 4|] includes 20 an output resistance 86 and an output potentiometer 87. A wire 88 connects. the arm of the potentiometer 81 to the primary 4| of the transformer 42.

The potentials necessary to operate the am- 5 plifier 21, the oscillator 40, the modulator 43, and the amplifier 4% are supplied by the customary batteries 85, 85 and 85.

The operation of the invention is as follows: The high frequency oscillator 40 produces a sup- 3 ply of constant frequency and voltage a portion of which, as determined by the setting of the potentiometer 81, is impressed on the grids of the pair of push-pull tubes of the modulator 43. The output of these push-pull tubes is controlled by a 35 direct current potential which is the envelope of the detected signal currents and is produced by amplifying a portion of the signal currents as at 27 and then rectifying said portion of the signal currents as at 13. The potential so produced is 40 applied across the condenser and the resistance This direct current potential is used to bias the push-pull tubes to control their output in proportion to the envelope of the signal currents. The output of the push-pull modulator is further amplified by the amplifying unit 46 and then rectified as at 52. This rectified current is used to unbalance the bridge circuit and allow the direct current voltage of the battery 6| or other constant source of direct current potential to displace the light valve in accordance to the amplitude of the signal currents.

From the foregoing description it will be apparent that I have provided a novel sound recording system which is simple in construction and highly efficient in use.

Having thus described my invention I claim:

1. In a circuit for controlling a sound recording device, a source of signal current, an amplifier for said signal current, means to rectify and partially filter said signal current, a high frequency oscillator having a constant output which is independent of external circuit conditions, a pushpull modulator including, a pair of grids, means to supply a small portion of the output of said high frequency oscillator to said modulator, means to apply said rectified signal current to both of said grids in the same phase whereby the unfiltered signal is suppressed and the signal amplitude component is applied as a bias to said modulator, an amplifier associated with said modulator and adapted to amplify the output thereof, and a rectifier torectify the output of said amplifier.

2. In a circuit for controlling a sound recording device, a source of signal current, an amplifier for said signal current, means to rectify and partially filter said signal current, a high frequency oscillator, a modulator including a pair of grids, means to supply a portion of the output of said high frequency oscillator to said modulator, means to apply said rectified signal current to both of said grids in the same phase whereby the unfiltered signal is suppressed and the signal amplitude component is applied as a bias to said modulator, and a rectifier to rectify the output of said modulator. V

PERCY R. GLENN. 

